Gas turbine engines commonly include an axial flow turbine that comprises at least one annular array of radially extending aerofoil blades mounted on a common disc. Each aerofoil blade is sometimes provided with a shroud at its radially outer tip so that the shrouds of adjacent blades cooperate to define a radially outer circumferential boundary to the gas flow over the aerofoil blades.
In operation, there can be a tendency for the gas flows over the aerofoil blades to cause the blades to vibrate to such an extent that they require some degree of damping. One way of achieving such damping is to interconnect the shrouds of the blades with a single length of wire that passes through appropriate circumferentially extending passages provided in the shrouds. Any vibration of the blades results in relative movement between their shrouds and hence between the passages and the wire. Friction between the passage walls and the wire tends to dampen such relative movement, and hence the blade vibration. Such an arrangement is described and shown in Swiss Patent No. 666326. The drawback with this type of arrangement, however, is that the wire adds undesirable weight to the blade assembly.
EP0806545B1 discloses a damper for damping non-synchronous vibration in adjacent shrouded aerofoil blades in the form of pin that locates in confronting passages in adjacent blade shrouds. The pin is provided with larger diameter portions that are located totally within the passages and frictionally engage the surfaces of the passages to provide vibration damping. The pin is circular in cross section and the larger diameter pin portions are interconnected by a central, thinner portion. The configuration of the pin reduces the likelihood of it wearing in such a manner that it jams in the passages and no longer provides vibration damping. However, during engine running the damper experiences excessive wear resulting in loss of material and a reduction in damper mass. Due to the small size of the damper, this mass loss constitutes a significant proportion of its mass. The reduction in damper mass causes damping effectiveness to be compromised with time, and can result in an in service failure.